The invention relates generally to the treatment of cancer by localized heating of the tumor cells using microwave radiation or other heating means and more specifically concerns accurately monitoring the temperature of subcutaneous tissue in the region of the tumor.
Nonsurgical elimination of malignant tumors has been approached using various techniques. Only limited success has been realized using chemotherapy and/or x-ray irradiation, and both techniques frequently elicit distressing side effects. In contrast, nonionizing microwave or ultrasonic energy are potential alternatives whose side effects may be less severe than those of ionizing radiation such as x-ray. Unlike chemotherapy which acts systematically, the side effects of microwave and ultrasound, if any, are localized. Microwave (1-10 GHz electromagnetic energy) and ultrasound waves (generally of Megahertz frequency) can be generated inexpensively without the cost, bulk, or hazards of the radiation and high voltage supplies required for x-ray.
Unlike x-ray irradiation, microwave and ultrasound destroy malignant cells strictly by localized heating of the affected region. Advantage is taken on the malignant cell's higher sensitivity to temperature relative to that of normal tissue. In addition, reduced destruction of healthy tissue is achieved by concentrating several different energy sources on the tumor region, as is done with x-ray. Significant malignant cell destruction occurs for temperatures above a threshold of 43.degree. C. Below this threshold, however, malignant cell growth may be accelerated. Thus, careful control of temperature must be maintained in the vicinity of the tumor: Too much energy may destroy surrounding healthy tissue; too little might aggravate tumor enlargement.
Noninvasive localized temperature sensing methods such as infrared detection of skin surface temperature and microwave thermometry have proved to be unreliable indicators of the temperature in underlying tissue such as the breast. Surgically implanted, invasive temperature probes are at risk of causing tumor metastasis; this constitutes a significant hazard, particularly for breast tumors which frequently are the site of the primary malignancy. Furthermore, such probes are an infection risk and cannot be used during irradiation without resulting in localized heating. Thus, a noninvasive but accurate method for measuring the temperature of underlying tissue is required if microwave or ultrasonic irradiation is to become a viable form of cancer treatment.
It is therefore an object of this invention to provide a noninvasive but accurate technique for measuring the temperature of underlying tissue.
Another object of this invention is to provide a technique based on ultrasound for measuring tissue temperature.
A further object of this invention is to provide a technique for measuring tissue temperature suitable for use with microwave or ultrasound treatment of cancer.
Still another object of the invention is to provide a technique for measuring tissue temperature which is safe enough to permit frequent, repeated measurements without accumulated exposure hazard to either the patient or the medical staff.
A still further object of the invention is to provide a noninvasive technique for measuring tissue temperature which is accurate to within 0.5.degree. C. over the range of 35.degree. C. to 45.degree. C.
Yet another object of this invention is to provide a noninvasive technique for measuring tissue temperature which is accurate over a wide range of temperatures.
Other objects and advantages of this invention will become apparent hereinafter in the specification and drawings.